1. Field of the Invention
The present invention relates to an analog image memory device using charge transfer.
2. Description of the Prior Art
At the present time the devices used for storing a video image are either memory tubes or large capacity digital memories. In the case of memory tubes, the information is stored directly in analog form whereas in the case of digital memories, it is necessary to transform the analog information into digital information, which requires very large storage capacity and a number of additional conversion devices. Now, a man skilled in the art knows that charge transfer devices are capable of storing and transporting information in analog form. However, the maximum storage time in a charge transfer device at ordinary temperature is of the order of 20 to 40 ms. Consequently, analog memories capable of storing charge amounts corresponding to the analog signal may be formed using charge transfer technology on condition that the information is cyclically regenerated. Such regeneration may be provided by means of analog-digital and digital-analog converters. It requires the storage of coded analog information, which may be readily obtained in the charge transfer technique by quantifying the charge packets corresponding to the analog information. Thus memories called multi-level analog memories can thus be formed.
As shown in FIG. 1, high capacity charge transfer memories capable of storing a video image at present available on the market are formed by:
an input register R.sub.21 of CCD type (charge coupled device) in which the information is introduced serially by successive shifts, PA1 parallel registers R.sub.P1 to R.sub.PN of CCD type in which the information contained in the input register is transferred simultaneously then shifted successively, and PA1 an output register R.sub.S2 of CCD type which receives the information conveyed by the registers in parallel and which transmits it serially by successive shifts to the output of the memory. PA1 a memory zone of N lines of M memory points, each memory point being formed by the integration on the same semi conductor substrate of an MIS capacity separated from a diode by a screen gate, PA1 means for selecting each memory point, PA1 means for writing in each memory point a charge amount corresponding to the analog signal to be stored, and PA1 means for reading, line by line, the memory zone after writing.
The main limitation of a series-parallel-series type organization such as described above is the large number of transfers to be effected on analog information. Consequently, the inefficiencies of the transfer limit to about 3 bits the accuracy of the coding, that is to say to 8 the number of levels stored by a CCD stage.